Lithographic plates



Oct. 6, 1959 c. F. GEEsE 2,907,656

LITHOGRAPHIC PLATES Filed NOV. 12, 1953 1.1mm a INVENTOR Cha ljes E 9 6 ATTOR United States Patent LITHOGRAPHIC PLATES Charles F. Geese, Old Greenwich, Conn., assignor, by

mesne assignments, to Chrome Steel Plate Corporation This invention relates to printing plates, particularly lithographic plates and to methods of lithographing. More particularly it relates to plates wherein the image or printing ink surfaces thereof are comprised of a clean or unoxidized ferrous metal such as a low carbon steel and the water receptive surfaces are comprised of passivated chrome plate. In another aspect, the invention may be said to lie in lithographing with such plates under circumstances wherein extremely large numbers of printing impressions may be made before the plate is appreciably worn and also wherein shutdowns of the press due to roller stripping, that is rejection of the printing ink by the press, riders and so on is minimized.

While prior attempts have been made to utilize iron or steel plates in various forms and in combinations with other metals, compounds and so on in order to take advantage of the potentialities of greater wear and lower cost which ferrous metals offer in the printing art, so far as I am presently informed these prior attempts have not been successful and have been subject to certain disadvantages.

It therefore is an object of the present invention to overcome the difliculties of known lithographic plates and methods of lithographing. It is another object of the invention to provide printing plates which are strong, inexpensive and which are capable of printing a great quantity of impressions with fine detail. It is a further object of the invention to provide improved and more eflicient methods of printing. Other objects of the invention will be in part pointed out and in part apparent as the specification proceeds.

Before describing my invention more fully it is to be noted that the subsequent description of specific details of embodiments of my invention is generally intended to be illustrative and not limiting or exhaustive of my invention, the boundaries of which are set forth with particularity in the appended claims.

In one of its broader aspects the invention may be said to lie in the discovery that a plate having excellent lithographic printing characteristics and good durability may be formed of ordinary steel plated with chromium, the chrome surfaces being in an ink repellent but water receptive condition and the image or printing surfaces being formed in clean steel significantly free of oxide or complex films. I found that although iron oxide films exhibit good ink receptivity as was known heretofore, plates of this type do not print well in long continued service, apparently due to minute flaking, breaking or distortion of the oxide films so that blind" printing occurs which of course 'is highly undesirable. Moreover, known printing plates of the oxide type, as well as the ordinary zinc and copper plates are also subject to roller stripping which results in press shutdowns in order to clean and reactivate the plate and roller surfaces so that they are again receptive to ink.

' Perhaps the features of the invention may best be understood and appreciated by reference to the subsequent description of a specific example of the invention and the accompanying drawings wherein:

Figure 1 is a simplified diagrammatic view of a typical offset printing press showing the relative positioning of the water and ink founts and their respective transfer rolls, the plate roll, the rubber blanket roll and the impression roll.

Figure 2 is a fragmentary cross-sectional view of a low carbon steel plate useful in making a printing plate according to the invention.

Figure 3 is a fragmentary cross-sectional view of the steel plate of Figure 2 after it has received a plating of chromium.

Figure 4 is a cross-sectional view of the plate of Figure 3 after it has received a coating of light sensitive and hardenable gum or gel.

Figure 5 is a side view of the plate of Figure 4 and illustrates the light hardened areas and the soft areas of the light sensitive coating after it has been exposed to a photographic film and a strong light to form the desired image thereon.

Figure 6 is a side view of the plate of Figure 5 after the soft gum has been removed from the image area of the plate and the image area cleaned or treated as set forth below.

Figure 7 is a side view of the plate of Figure 6, illustrating the presence of a tenacious protective bond 24a of ink, varnish or asphalt and the like on the image areas and the removal of the light hardened gum from the water receptive chrome plated areas.

Referring more particularly to the drawings, a typical offset printing press 11 is shown having a plate press roll 12 which receives ink from fount 13 by the transfer rolls or riders 14 and which receives moistening water from water fount 15 by means of transfer rolls or riders 16. Rubber blanket roll 17 picks up the ink impression from press roll 12. Paper 19, carried by rollers 20,

used) is first brightened on one side by polishing it with pumice powder or another fine abrasive in a dilute solution of hydrochloric acid. For example, I find a solution of only 4 ounces of hydrochloric acid to one gallon of water to be satisfactory.

This cleaned and brightened plate 21 is next washed with water and immersed in a chromium plating bath (not shown) which is of'standard composition. Typically such a bath will contain about 30 to 50 ounces of chromic acid per gallon and about 0.3 to 0.5 ounce of sulfuric acid per gallon so that the chromate-sulfate ratio is about to 1. Some 6 to 8 volts are applied and a current density of approximately 1% amperes per square inch of 'plate is maintained; I get good results by initially reversing the current so that the plate 21 first is used as an anode for a short period of about half a minute. Then the current is maintained in the normal direction until a thin chrome coating is applied to the plate. For most operations, a chrome thickness of about 0.0030 inch is sufficient. The plating bath is maintained at about F. while the desired coating is being attained. This yields a dull finish chrome coating 22 on plate 21, as shown in Figure 3.

As a next step, I coat the chromed plate 21 of Figure 3 with a light hardenable resist material 23 which is cur,- rently used in the lithographic art in connection with zinc lithographic plates. Specifically I prefer a deep etch face.

a small amount of water, e.g. 3 ounces.

'ing of varnish or the like with a sutable solvent.

hardened areas 23a (see Fig. 5) and soft areas 23 which are the image areas. These soft or image'areas 23 are jthen washed away with water to remove the soft resist therefrom.

Next I etch the image areas which were under the soft resist 23 with a standard etching solution such as hydrochloric acid or calcium chloride mixtures to remove the exposed portions of the chrome plate 22' and to yield the desired image etched in the exposed grainy steel sur- At this point in the treatment, the plate 21 is in the condition as depicted in Figure 6.

-After the plate has been freed of the soft resist and the exposed chrome plate and the image has been etched into the steel, I subject the plate to a cleaning treatment. In the presently preferred form, I dissolve about 2 ounces of ferric chloride and 2 ounces of ammonium chloride in To this solution is added 1%. ounces of insoluble bismuth chloride, ounces of ethyl alcohol and a small quantity of pumice powder. This mixture is then rubbed briskly for about one minute with felt pads over the surfaces of plate 21. This operation results in effective cleaning of the steel image surfaces so that they appear silvery bright, yet without deleteriously affecting the chrome surfaces because of the protection of the hardened gum bicromated coating on the non-printing areas.

It is to be noted that although I prefer the specific cleaning mixture set forth above, other materials may also be used so long as they are not so abrasive that the light hardened surface is injured while the cleaning mixture is applied to the image areas and so long as the use of oxidants which will yield oxide or other complex films on the exposed ferrous surfaces is avoided.

While the cleaned plate is still wet, I remove the residual cleaning mixture by washing the plate with a mixture of ethyl alcohol and a hydrocarbon lacquer thinner. Then there is applied to the plate a protective layer 24a of thin varnish or the like, any excess thereon being wiped off with rags or by similar means. Th s varnish layer protects the ferrous image areas from oxidation or other contamination while the light hardened coating over the chrome non-image areas is being removed.

After protecting the etched image area 24 as indicated above, I then wash off the light hardened resist material 23a which is over the chrome plate areas 22 by immersing plate 21 in a solution of any good detergent or even in a weak acid such as dilute citric acid.

I then dry the plate and remove the protective coat- Next I apply a conventional rub-up ink to the plate, after using a dilute solution of ortho phosphoric acid which serves to keep the chrome non-image areas passivated or nonreceptive to ink while the ink is applied into the image. Apparently, also the dilute ortho phosphoric acid avoids or minimizes unwanted oxidation of the ferrous printing area.

For storage and protection against handling a protective coating of gum arabic is finally applied to the plate which may easily be removed when the plate is to be placed on the press for printing. Again. if the plate is to be used for printing a color which is different from the conventional black rub-on ink, this ink may also be removed with a thin varnish or the like reduced with a solvent such as turpentine thereby also protecting the image areas from contamination or oxidation.

As indicated above, a feature of the present invention lies in the manner of printing with the plates described,

aeoaeae- At the present time, considerable difliculty occurs in using known Zinc, aluminum or copper plates, particularly with regard to press shut-downs. In many instances after a number of printing impressions has been made, the press roll, riders, steel drums and so on refuse to accept ink and the so-called roller stripping occurs. It is common practice when this occurs 'to shut down the press in order to clean residual ink, moisture, emulsions thereof and the like from the press equipment with a variety of cleaning formulations in order to reactivate the ink receptive surfaces. This entails a considerable expense due to labor costs and due to loss of press efiiciency.

I have found that roller stripping and blind printing may be greatly minimized in contrast to present difficulties by incorporating into the fount 15 bland compounds or materials which apparently function to keep the image areas of the plate clean and free of undesirable metal films. For example, I have found that a material such as glycerine is quite useful when employed in low concentrations. In a specific embodiment of this phase of the invention, I add one ounce of glycerine to about 3 gallons of fount water, together with about one eighth of an ounce of ammonium bichromate to keep the chrome plate areas clean and water receptive. Using lithographic plates according to the invention as heretofore described and with this treated fount water, I have avoided both roller stripping and blind printing for very long printing runs.

Hav ng now described my invention, what I claim is:

1. The process of making a lithographic plate which comprises the steps of cleaning a steel plate capable of being made oleophilic, applying a thin coating of chro mium to said plate in a chrome plating bath maintained at a high current density, then coating a chromed side of said plate with a light sensitive and light hardenable esist material, forming on said plate an image comprising areas to be ink-printed and areas not to be ink printed by passing light through a film bearing said image while said film is positioned adjacent to said lithographic plate, removing unhardened resist material from the plate, chrome etching said plate with a standard acidic etching material to thereby remove exposed chromium, whereby areas to be ink-printing are produced in the steel plate corresponding with those areas of the image to be inkprinted, next cleaning the ink-printing areas by rubbing on the plate a cleaning material comprising an aqueous solution of about two parts by weight each of ferric chloride and ammonium chloride in about three parts by weight of water, mixed with a solution of about 1 /2 parts by weight of bismuth chloride, and pumice powder, in about ten parts by weight of an alcohol, which leaves the ink-printing areas of the plate bright and silvery in appearance, thereafter removing residual cleaning material with an organic solvent comprising ethyl alcohol, applying a thin coating of lithographic varnish to the plate to protect the ink-printing areas thereof, next washing from the plate light hardened resist material, then drying said plate and removing the varnish layer, applying a rub-up ink which preferentially adheres to the ink-printing areas after a passivating agent for the chrome areas of the'plate, and finally applying a protective gum coating to the plate.

2. The process of making a lithographic plate which comprises the steps of cleaning a low carbon steel plate, briefly subjecting said plate to the influence of electric current while said plate is immersed in a standard chrome plating bath wherein said plate initially is maintained as the anode, then reversing the current and applying a thin coating of chromium to said plate in a chrome plating bath maintained at a high current density, then coating a chromed side of said plate with a light sensitive and light hardenable resist material, forming on said plate and image comprising areas to be ink-printed and areas not to be ink-printed by passing light through a film bearing said image while said film is positioned adjacent to said lithographic plate, removing unhardened resist, material from the plate, etching said plate with astandard acidic chrome etching material to thereby remove exposed chromium,,whereby areas to be ink-printing are produced in the steel plate corresponding with those areas of the image to be ink-printed, next cleaning the ink-printing areas by rubbing on the plate a cleaning material comprising an aqueous solution of about two parts by weight each of ferric chloride and ammonium ,chloride in about three parts by weight of water, mixed .with a solution of about 1 /2 parts by weight of bismuth chloride, and pumice powder, in about ten parts by weight of a lower alcohol, which leaves the ink-printing areas of the plate bright and silvery in appearance, thereafter removing residual cleaning material with an organic solvent comprisingethyl alcohol, next coating the plate with a thin varnish coating to protect the ink-printing area, then washing from the plate light hardened resist material, drying the plate and removing the varnish with a suitable solvent, hen applying a rub-up ink after a passivating agent comprising dilute orthophosphoric acid to the plate to thereby preferentially coat the ink-printing areas with ink and to render the chrome areas inkrepellent..

3. The process of making a lithographic plate which comprises the steps of cleaning a low carbon steel plate, applying a thin coating of chromium to said plate in a chrome plating bath maintained at a high current density, then coating a chromed side of said plate with a light sensitive and light hardenable resist material, forming on said plate an image comprising areas to be ink-printed and areas not to be ink-printed by passing light through a film bearing said image while said film is positioned adjacent to said lithographic plate, removing unhardened resist material from the plate, etching said plate with a standard acidic chrome etching material to thereby remove exposed chromium, whereby areas to be ink-printing are produced in the ferrous metal of the plate corresponding with those areas of the image to be ink-printed, next cleaning the ink-printing areas by rubbing on the plate a cleaning material comprised of a mixture of about equal parts by weight each of ferric chloride, ammonium chloride, and bismuth chloride, and a mild abrasive powder dispersed in slightly aqueous ethyl alcohol which thereby leaves the ink-printing areas of the plate bright and silvery in appearance, thereafter removing residual cleaning material with a mixed ethyl alcohol and light hydrocarbon solvent, applying a thin protective resin coating to the plate, next washing from the plate light hardened resist material, then drying the plate and re moving the resin coating, next applying a passivating agent comprising dilute orthophosphoric acid and a rubup ink to the plate to thereby coat the ink-printing area with ink and to render the chrome areas water receptive and ink repellent, and finally applying a protective gum coating to the inked plate.

4. The process of making a lithographic plate which comprises the steps of cleaning a low-carbon steel plate, applying a thin dull coating of chromium to said plate in a chrome plating bath maintained at a high current density, then coating a chromed side of said plate with a light sensitive and light hardenable resist material, forming on said plate an image comprising areas to be inkprinted and areas not to be ink-printed by passing light through a film bearing said image while said film is positioned adjacent to said lithographic plate, removing unhardened resist material from the plate, etching said plate with a standard acidic chrome etching material to thereby remove exposed chromium, whereby areas to be inkprinting are produced in the ferrous metal of the plate corresponding with those areas of the image to be inkprinted, next cleaning the ink-printing areas by rubbing on the plate a cleaning material comprised of a mixture of about two parts by weight each of ferric chloride, ammonium chloride, and bismuth chloride, and a mild abrasive powder dispersed in about 13 parts by weight of slightly aqueous ethyl alcohol which thereby leaves-the ink-printing areas of the plate bright and silvery in appearance, thereafter removing residual cleaning material with an organic solvent comprisedof ethyl alcohol and a light hydrocarbon, applying a thin protective coating of varnish to the plate, next washing from the plate light hardened resist material, then after drying the plate and removing varnish therefrom, nextfapplying rub-up ink after a passivating agent comprised of dilute orthophosphoric acid to the plate, and finally applying a protective coating of gum arabic to the plate to protect the oleophilic properties of the ink-printing areas,

5. The process of making a lithographic plate which comprises the steps of cleaning a low-carbon steel plate, applying a thin coating of chromium to said plate in a chrome plating bath maintained at a high current density, then coating a chromed side of said plate with a light sensitive and light hardenable resist material, forming on said plate an image comprising areas to be ink-printed and areas not to be ink-printed by passing light through a film bearing said image, while said film is positioned adjacent to said lithographic plate, removing unhardened resist material from the plate, etching said plate with a standard acidic chrome etching material to thereby remove exposed chromium, whereby areas to be ink-printing are produced in the ferrous metal of the plate corresponding with those areas of the image to be ink-printing, next cleaning the ink-printing areas by rubbing on the plate a cleaning material comprised of a mixture of about two parts by weight each of ferric chloride, ammonium chloride, and bismuth chloride, and a mild abrasive powder dispersed in about 13 parts by weight of slightly aqueous ethyl alcohol, which leaves the inkprinting areas of the plate bright and silvery in appearance, thereafter removing residual cleaning material with a mixed ethyl alcohol and light hydrocarbon solvent, applying a protective thin resin coating to the plate, next washing from the plate light hardened resist material with an aqueous detergent solution, drying the plate and removing the resin layer, then rubbing the plate with rubup ink and a dilute phosphoric acid passivating agent, and finally applying a protective coating such as gum arabic to the plate to protect the oleophilic properties of the steel plate.

6. The process according to claim 5 wherein said chrome plating bath is maintained at about F.

7. The process of making a lithographic plate which comprises the steps of cleaning a low carbon steel plate, briefly subjecting said plate to the influence of electrical current while said plate is immersed in a standard chrome plating bath wherein said plate initially is maintained as the anode, then reversing the current and applying a thin coating of chromium to said plate in a chrome plating bath maintained at a high current density, then coating a chromed side of said plate with a light sensitive and light hardenable resist material, forming on said plate an image comprising areas to be ink-printed and areas not to be ink-printed by passing light through a photographic film bearing said image while said photographic film is positioned adjacent to said lithographic plate, removing unhardened resist material from the plate, etching said plate with a standard acidic chrome etching material to thereby remove exposed chromium, whereby areas to be ink-printing are produced in the ferrous metal of the plate corresponding with those areas of the image to be ink-printed, next cleaning the ink-printing areas by rubbing on the plate a cleaning material comprised of a mixture of about two parts by weight. each of ferric chloride, ammonium chloride, and bismuth chloride, and a mild abrasive powder dispersed in about 13 parts by weight of slightly aqueous ethyl alcohol which thereby leaves the ink-printing areas of the plate bright and silvery in appearance, thereafter removing residual cleaning material with an organic solvent comprised of ethyl alcohol and a light hydrocarbon, applying a protective -"c'oating'of thin lithographic varnish to the plate, next washing' from the plate light hardened resist material with an aqueous detergent solution, then drying the plate and removing the varnish, then passivating the chrome .areas of the plate and applying a rub-0n ink to the inkprinting areas.

References Cited in the file of this patent I UNITED STATES PATENTS 1,069,856 Cornwall Aug. 12, 1913 1,151,459 Hatt l Aug. 24, 1915 Great Britain Sept. 14, 1949 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,907,656

October 6 1959 Charles F, Geese patent requiring correction Letters Patent should read as corrected below Column 4, line 72,

claim 2, for "and" first occurrence read an column 5, line l9 same claim 2, for "hen" read then column 6, line and comma "ing," read ed,

28, claim 5, for the syllable Signed and sealed this 21st day of June 1960,

'(SEAL) At'Eest:

KARL H. AXLINE ROBERT c. WATSON Atte stlng offlcer Conmissioner of Patents 

1. THE PROCESS OF MAKING A LITHOGRAPHIC PLATE WHICH COMPRISES THE STEPS OF CLEANING A STEEL PLATE CAPABLE OF BEING MADE OLEOPHILIC, APPLYING A THIN COATING OF CHROMIUM TO SAID PLATE IN A CHROME PLATING BATH MAINTAINED AT A HIGH CURRENT DENSITY, THEN COATING A CHROMED SIDE OF SAID PLATE WITH A LIGHT SENSITIVE AND LIGHT HARDENABLE RESIST MATERIAL, FORMING ON SAID PLATE AN IMAGE COMPRISING AREAS TO BE INK-PRINTED AND AREAS NOT TO BE INK PRINTED BY PASSING LIGHT THROUGH A FILM BEARING SAID IMAGE WHILE SAID FILM IS POSITIONED ADJACENT TO SAID LITHOGRAPHIC PLATE, REMOVING UNHARDENED RESIST MATERIAL FROM THE PLATE, CHROME ETCHING SAID PALTE WITH A STANDARE ACIDIC ETCHING MATERIAL TO THEREBY REMOVE EXPOSED CHAROMIUM, WHEREBY AREAS TO BE INK-PRINTING ARE PRODUCED IN THE STEEL PLATE CORRESPONDING WITH THOSE AREAS OF TEH IMAGE OT BE INKPRINTED, NEXT CLEANING THE INK-PRINTING AREAS BY RUBBING ON THE PLATE A CLEAINING MATERIAL COMPRISING AN AQUEOUS SOLUTION OF ABOUT TWO PARTS BY WEIGHT EACH OF FERRIC CHLORIDE AND AMMONIUM CHLORIDE IN ABOUT THREE PARTS BY WEIGHT OF WATER, MIXED WITH A SOLUTION OF ABOUT 1 1/2 PARTS BY WEIGHT OF BISMUTH CHLORIDE, AND PUMICE POWDER, IN ABOUT TEN PARTS BY WEIGHT OF AN ALCOHOL, WHICH LEAVES THE INK-PRINTING AREAS OF THE PLATE BRIGHT AND SILVERY IN APPEARANCE, THEREAFTER REMOVNG RESIDUAL CLEANING MATERIAL WITH AN ORGANIC SOLVENT COMPRISNG ETHYL ALCOHOL, APPLYING A THIN COATING OF LITHOGRAPHIC VARNISH TO THE PLATE TO PROTECT THE INK-PRINTING AREAS THEREOF, NEXT WASHING FROM THE PLATE LIGHT HARDENED RESIST MATERIAL, THEN DRYING SAID PLATE AND REMOVING THE VARNISH LAYER, APPLYING A RUB-UP INK WHICH PREFERENTIALLY ADHERES TO THE INK-PRINTING AREAS AFTER A PASSIVATING AGENT FOR THE CHROME AREAS OF THE PLATE, AND FINALLY APPLLYING A PROTECTIVE GUM COATING TO THE PLATE. 